1. Field of the Invention
The present invention relates to a cutter device for use in a lawn mower, and more particularly to a cutter device comprising a pair of vertically superposed cutter blades that is rotatable in a substantially horizontal plane.
2. Description of the Prior Art
One conventional lawn mower has a downwardly opening cutter housing and a pair of cutter blades that is housed in the cutter housing and rotatable in a substantially horizontal plane. The cutter blades are vertically superposed one on the other. The upper cutter blade is positioned forwardly of the lower cutter blade in the direction in which they rotate, for clipping the grass twice to eliminate any region where the grass remains uncut. Such prior lawn mower is disclosed in U.S. Pat. No. 2,760,327 and Japanese utility model publication No. 64-6035.
The grass which remains uncut by the upper cutter blade is forcibly pressed down by an air flow caused by the upper cutter blade. Therefore, the remaining grass that is pressed down may not effectively be clipped by the lower cutter blade that follows the upper cutter blade. As a result, the lawn that is mowed by the lawn mower may not neatly be finished. Moreover, if the inner surface of the cutter housing is not properly spaced from the circular path of the outermost ends of the cutter blades, then the gap between the inner surface of the cutter housing and the outermost ends of the cutter blades may possibly be clogged with grass clippings, or grass clippings may possibly fall together and form grass clipping ridges on the lawn along the direction in which the lawn mower moves forwardly.